Method for manufacturing an electro-optical device

ABSTRACT

An object of the present invention is to provide an EL display device having high operation performance and reliability.  
     A third passivation film  45  is disposed under the EL element  203  comprising a pixel electrode (anode)  46,  an EL layer  47  and a cathode  48,  and diffusion of alkali metals from the EL element  203  formed by ink jet method into TFTs is prevented. Further, the third passivation film  45  prevents penetration of moisture and oxygen from the TFTs, and suppress degradation of the EL element  203  by dispersing the heat generated by the EL element  203.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an electro-optical device, typically anEL (electroluminescence) display device formed by a semiconductorelement (an element using a semiconductor thin film) made on asubstrate, and to electronic equipment (an electronic device) having theelectro-optical device as a display (also referred to as a displayportion). In particular, the present invention relates to amanufacturing method thereof.

2. Description of the Related Art

Techniques of forming a TFT on a substrate have been widely progressingin recent years, and developments of applications to an active matrixtype display device are advancing. In particular, a TFT using apolysilicon film has a higher electric field effect mobility (alsoreferred to as mobility) than a TFT using a conventional amorous siliconfilm, and high speed operation is therefore possible. As a result, itbecomes possible to perform pixel control, conventionally performed by adriver circuit external to the substrate, by a driver circuit formed onthe same substrate as the pixel.

This type of active matrix display device has been in the spotlightbecause of the many advantage which can be obtained by incorporatingvarious circuits and elements on the same substrate in this type ofactive matrix display device, such as reduced manufacturing cost, smallsize, increased yield, and higher throughput.

Switching elements are formed by a TFT for each of the pixels in theactive matrix display device, current control is performed by driverelements using the switching elements, and an EL layer(electroluminescence layer) is made to emit light. A typical pixelstructure at this time is disclosed in, for example, U.S. Pat. No.5,684,365 (Japanese Patent Application Laid-open No. 8-234683) andJapanese Patent Application Laid-open No. Hei 10-189252.

In performing color display of these EL display devices, trials fordisposing EL layers that emit three primary colors of red (R), green (G)and blue (B) on respective pixels have been made. However, most of thematerials used in general as EL layers are organic materials and thepatterning is extremely difficult. This is because EL materialsthemselves are very weak to moisture, and it is difficult to treat themas they easily dissolve even in a developing solution.

As a technology for solving such a problem, a technique of forming ELlayers by ink jet method is suggested. For example, an active matrix ELdisplay in which EL layers are formed ink jet method is disclosed inJapanese Patent Application Laid-Open No. Hei 10-012377. Further,similar technique is also disclosed in Shimada, T. et al., SID 99DIGEST, P376-9, “Multicolor Pixel Patterning of Light-Emitting Polymersby Ink-jet Printing.”

However, because ink jet method is performed under normal pressure, itis disadvantageous in the point that contaminants in the externalatmosphere are easily taken. Namely, it has a problem that because ELlayers are formed in a state of easily including mobile ions such asalkaline metals, diffusion of the alkaline metals therefore can givefatal damage to the TFTs. Note that throughout the Specificationalkaline metals and alkali-earth metals are together referred to as“alkaline metals”.

SUMMARY OF THE INVENTION

The present invention is made in view of the above problems, and anobject of the present invention is to provide a method for manufacturingan electro-optical device having good operation performance and highreliability, and in particular, to provide a method for manufacturing anEL display device. Another object of the present invention is toincrease the quality of electronic equipment (an electronic device)having the electro-optical device as a display by increasing the imagequality of the electro-optical device.

In order to achieve the above objects, diffusion of alkaline metals fromthe EL elements that are formed by ink jet method is prevented by aninsulating film (passivation film) disposed between the EL elements andTFTs in the present invention. In concrete, an insulating film that iscapable of preventing penetration of alkaline metals is disposed over aleveling film that covers TFTs. Namely one with sufficiently smallalkaline metal diffusion speed at an operation temperature of the ELdisplay device (typically from 0 to 100° C.) may be used as theinsulating film.

More preferably, an insulating film that do not penetrate moisture andalkaline metals and that has high pyroconductivity (high radiatingeffect), and dispose the insulating film in contact with the EL elementsor more preferably surround the EL elements by such insulating film. Inother words, an insulating film that is effective for blocking themoisture and alkaline metals and that has radiation effect is disposedto the nearest position possible to the EL elements, and preventdegradation of the EL elements by the insulating film.

Further, in case that such insulating film cannot be used as a singlelayer, a laminate of an insulating film having blocking effect againstmoisture and alkaline metals and an insulating film having radiatingeffect can be used.

In any ways, measures to protect the TFTs that drive the EL elementsthoroughly from alkaline metals are required in case of forming an ELlayer by ink jet method, and further in order to prevent degradation ofEL layer itself (it can also be referred to as degradation of ELelement), measures against both moisture and heat should be consideredat the same time.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a diagram showing the cross sectional structure of the pixelportion of an EL display device of the present invention;

FIGS. 2A and 2B are diagrams showing the top view and the composition,respectively, of the pixel portion of an EL display device of thepresent invention;

FIGS. 3A to 3E are diagrams showing manufacturing processes of an activematrix type EL display device of Embodiment 1;

FIGS. 4A to 4D are diagrams showing manufacturing processes of an activematrix type EL display device of Embodiment 1;

FIGS. 5A to 5C are diagrams showing manufacturing processes of an activematrix type EL display device of Embodiment 1;

FIG. 6 is a diagram showing an external view of an EL module ofEmbodiment 1;

FIG. 7 is a diagram showing the circuit block structure of an EL displaydevice of Embodiment 1;

FIG. 8 is an enlarged diagram of the pixel portion of an EL displaydevice of the present invention;

FIG. 9 is a diagram showing the element structure of a sampling circuitof an EL display device of Embodiment 1;

FIG. 10 is a diagram showing the composition of the pixel portion of anEL display device of Embodiment 2;

FIG. 11 is a diagram showing the cross sectional structure of an ELdisplay device of Embodiment 3;

FIGS. 12A and 12B are diagrams showing the top view and the composition,respectively, of the pixel portion of an EL display device of Embodiment4;

FIG. 13 is a diagram showing the cross sectional structure of the pixelportion of an EL display device of Embodiment 5;

FIG. 14 is a diagram showing the cross sectional structure of the pixelportion of an EL display device of Embodiment 8;

FIGS. 15A and 15B are diagrams showing the top view and the composition,respectively, of the pixel portion of an EL display device of Embodiment8;

FIGS. 16A to 16F are diagrams showing specific examples of electronicequipment of Embodiment 17;

FIGS. 17A and 17B are diagrams showing external views of an EL module ofEmbodiment 1;

FIGS. 18A to 18C are diagrams showing manufacturing processes of acontact structure of Embodiment 1;

FIGS. 19A to 19D are diagrams for explaining ink jet method of thepresent invention;

FIG. 20 is a diagram showing EL layer formation by ink jet method of thepresent invention;

FIG. 21 is a diagram showing laminate structure of EL layers ofEmbodiment 1;

FIGS. 22A and 22B are diagrams showing specific examples of electronicdevices of Embodiment 17;

FIGS. 23A and 23B are diagrams showing the circuit composition of thepixel portion of an EL display device of Embodiment 11;

FIGS. 24A and 24B are diagrams showing the circuit composition of thepixel portion of an EL display device of Embodiment 12; and

FIG. 25 is a diagram showing the cross sectional structure of the pixelportion of an EL display device of Embodiment 14.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment Mode

FIGS. 1 to 2B are used in explaining the preferred embodiment modes ofthe present invention. Shown in FIG. 1 is a cross sectional diagram of apixel of an EL display device of the present invention, in FIG. 2A isits top view, and in FIG. 2B is a circuit composition. In practice, apixel portion (image display portion) is formed with a multiple numberof this type of pixel arranged in a matrix state.

Note that the cross sectional diagram of FIG. 1 shows a cross sectioncut along the line A-A′ in the top view shown in FIG. 2A. Common symbolsare used in FIG. 1 and in FIGS. 2A and 2B, and therefore the threefigures may be referenced as appropriate. Furthermore, two pixels areshown in the top view of FIG. 2A, and both have the same structure.

Reference numeral 11 denotes a substrate, and reference numeral 12denotes an insulating film that becomes a base film (hereinafterreferred to as base film). A glass substrate, a glass ceramic substrate,a quartz substrate, a silicon substrate, a ceramic substrate, a metallicsubstrate, or a plastic substrate (including a plastic film) can be usedas the substrate 11.

Further, the base film 12 is especially effective for cases in which asubstrate containing mobile ions, or a substrate having conductivity, isused, but need not be formed for a quartz substrate. An insulating filmcontaining silicon may be formed as the base film 12. Note that the term“insulating film containing silicon” indicates, specifically, aninsulating film that contains silicon, oxygen, and nitrogen inpredetermined ratios such as a silicon oxide film, a silicon nitridefilm, or a silicon nitride oxide film (denoted by SiO_(x)N_(y)).

Further, it is effective to release the generated heat by TFTs by givingradiation effect to the base film 12 in preventing degradation of TFTsand degradation of EL elements. All of the known materials can be usedfor giving radiating effect.

Two TFTs are formed within the pixel here. Reference numeral 201 denotesa TFT functioning as a switching element (hereafter referred to as aswitching TFT), and reference numeral 202 denotes a TFT functioning as acurrent control element for controlling the amount of current flowing toan EL element (hereafter referred to as a current control TFT), and bothare formed by an n-channel TFT.

The field effect mobility of the n-channel TFT is larger than the fieldeffect mobility of a p-channel TFT, and therefore the operation speed isfast and large electric current can flow easily. Further, even with thesame amount of current flow, the n-channel TFT can be made smaller. Theeffective surface area of the display portion therefore becomes largerwhen using the n-channel TFT as a current control-TFT, and this ispreferable.

The p-channel TFT has the advantages that hot carrier injectionessentially does not become a problem, and that the off current value islow, and there are already reports of examples of using the p-channelTFT as a switching TFT and as a current control TFT. However, by using astructure in which the position of an LDD region differs, the problemsof hot carrier injection and the off current value in the n-channel TFTare solved by the present invention. The present invention ischaracterized by the use of n-channel TFTs for all of the TFTs withinall of the pixels.

Note that it is not necessary to limit the switching TFT and the currentcontrol TFT to n-channel TFTs in the present invention, and that it ispossible to use p-channel TFTs for either the switching TFT, the currentcontrol TFT, or both.

The switching TFT 201 is formed having: an active layer comprising asource region 13, a drain region 14, LDD regions 15 a to 15 d, a highconcentration impurity region 16, and channel forming regions 17 a and17 b; a gate insulating film 18; gate electrodes 19 a and 19 b, a firstinterlayer insulating film 20, a source wiring 21, and a drain wiring22.

As shown in FIG. 2A, the present invention is characterized in that thegate electrodes 19 a and 19 b become a double gate structureelectrically connected by a gate wiring 211 which is formed by adifferent material (a material having a lower resistance than the gateelectrodes 19 a and 19 b). Of course, not only a double gate structure,but a so-called multi-gate structure (a structure containing an activelayer having two or more channel forming regions connected in series),such as a triple gate structure, may also be used. The multi-gatestructure is extremely effective in lowering the value of the offcurrent, and by making the switching TFT 201 of the pixel into amulti-gate structure with the present invention, a low off current valuecan be realized for the switching TFT.

The active layer is formed by a semiconductor film containing a crystalstructure. In other words, a single crystal semiconductor film may beused, and a polycrystalline semiconductor film or a microcrystallinesemiconductor film may also be used. Further, the gate insulating film18 may be formed by an insulating film containing silicon. Additionally,any conducting film can be used for the gate electrodes, the sourcewiring, and the drain wiring.

In addition, the LDD regions 15 a to 15 d in the switching TFT 201 areformed so as not to overlay with the gate electrodes 19 a and 19 b byinterposing the gate insulating film 18. This structure is extremelyeffective in reducing the off current value.

Note that the formation of an offset region (a region that comprises asemiconductor layer having the same composition as the channel formingregions, and to which a gate voltage is not applied) between the channelforming regions and the LDD regions is more preferable for reducing theoff current value. Further, when a multi-gate structure having two ormore gate electrodes is used, the high concentration impurity regionformed between the channel forming regions is effective in lowering thevalue of the off current.

By thus using the multi-gate structure TFT as the switching TFT 201, asabove, a switching element having a sufficiently low off current valueis realized by the present invention. The gate voltage of the currentcontrol element can therefore be maintained for a sufficient amount oftime (for a period from one selection until the next selection) withoutdisposing a capacitor such as one shown in FIG. 2 of Japanese PatentApplication Laid-Open No. Hei 10-189252.

Namely, it becomes possible to eliminate the capacitor which causes areduction in the effective luminescence surface area, and it becomespossible to increase the effective luminescence surface area. This meansthat the image quality of the EL display device can be made brighter.

Next, the current control TFT 202 is formed having: an active layercomprising a source region 31, a drain region 32, an LDD region 33, anda channel forming region 34; a gate insulating film 18; a gate electrode35; the first interlayer insulating film 20; a source wiring 36; and adrain wiring 37. Note that the gate electrode 35 has a single gatestructure, but a multi-gate structure may also be used.

As shown in FIGS. 2A and 2B, the drain of the switching TFT iselectrically connected to the gate of the current control TFT.Specifically, the gate electrode 35 of the current control TFT 202 iselectrically connected to the drain region 14 of the switching TFT 201through the drain wiring (also referred to as a connection wiring) 22.Further, the source wiring 36 is connected to an electric current supplywiring 212.

A characteristic of the current control TFT 202 is that its channelwidth is larger than the channel width of the switching TFT 201. Namely,as shown in FIG. 8, when the channel length of the switching TFT istaken as L1 and its channel width as W1, and the channel length of thecurrent control TFT is taken as L2 and its channel width as W2, arelational expression is reached in which W2/L2≧5×W1/L1 (preferablyW2/L2≦10×W1/L1). Consequently, it is possible for more current to easilyflow in the current control TFT than in the switching TFT.

Note that the channel length L1 of the multi-gate structure switchingTFT is the sum of each of the channel lengths of the two or more channelforming regions formed. A double gate structure is formed in the case ofFIG. 8, and therefore the sum of the channel lengths L1 a and L1 b,respectively, of the two channel-forming regions becomes the channellength L1 of the switching TFT. That is, L1=L1 a+L1 b.

The channel lengths L1 and L2, and the channel widths W1 and W2 are notspecifically limited to a range of values with the present invention,but it is preferable that W1 be from 0.1 to 5 μm (typically between 1and 3 μm), and that W2 be from 0.5 to 30 μm (typically between 2 and 10μm). It is preferable that L1 be from 0.2 to 18 μm (typically between 2and 15 μm), and that L2 be from 0.1 to 50 μm (typically between 1 and 20μm) at this time.

Note that it is preferable to set the channel length L in the currentcontrol TFT on the long side in order to prevent excessive current flow.Preferably, W2/L2≧3 (more preferably W2/L2≧5). It is also preferablethat the current flow per pixel is from 0.5 to 2 μA (better between 1and 1.5 μA).

By setting the numerical values within this range, all standards, froman EL display device having a VGA class number of pixels (640×480) to anEL display device having a high vision class number of pixels(1920×1080) can be included.

Furthermore, the length (width) of the LDD region formed in theswitching TFT 201 is set from 0.5 to 3.5 μm, typically between 2.0 and2.5 μm.

The EL display device shown in FIG. 1 is characterized in that the LDDregion 33 is formed between the drain region 32 and the channel formingregion 34 in the current control TFT 202. In addition, the LDD region 33has both a region which overlaps, and a region which does not overlapthe gate electrode 35 by interposing a gate insulating film 18.

The current control TFT 202 supplies a current for making the EL element203 luminesce, and at the same time controls the amount supplied andmakes gray scale display possible. It is therefore necessary that thereis no deterioration when the current flows, and that steps are takenagainst deterioration due to hot carrier injection. Furthermore, whenblack is displayed, the current control TFT 202 is set in the off state,but if the off current value is high, then a clean black color displaybecomes impossible, and this invites problems such as a reduction incontrast. It is therefore necessary to suppress the value of the offcurrent.

Regarding deterioration due to hot carrier injection, it is known that astructure in which the LDD region overlaps the gate electrode isextremely effective. However, if the entire LDD region is made tooverlap the gate electrode, then the value of the off current rises, andtherefore the applicant of the present invention resolves both the hotcarrier and off current value countermeasures at the same time by anovel structure in which an LDD region which does not overlap the gateelectrode is formed in series.

The length of the LDD region which overlaps the gate electrode may bemade from 0.1 to 3 μm (preferable between 0.3 and 1.5 μm) at this point.If it is too long, then the parasitic capacitance will become larger,and if it is too short, then the effect of preventing hot carrier willbecome weakened. Further, the length of the LDD region not overlappingthe gate electrode may be set from 1.0 to 3.5 μm (preferable between 1.5and 2.0 μm). If it is too long, then a sufficient current becomes unableto flow, and if it is too short, then the effect of reducing off currentvalue becomes weakened.

A parasitic capacitance is formed in the above structure in the regionwhere the gate electrode and the LDD region overlap, and therefore it ispreferable that this region not be formed between the source region 31and the channel forming region 34. The carrier (electrons in this case)flow direction is always the same for the current control TFT, andtherefore it is sufficient to form the LDD region on only the drainregion side.

Further, looking from the viewpoint of increasing the amount of currentthat is able to flow, it is effective to make the film thickness of theactive layer (especially the channel forming region) of the currentcontrol TFT 202 thick (preferably from 50 to 100 nm, more preferablybetween 60 and 80 nm). Conversely, looking from the point of view ofmaking the off current value smaller for the switching TFT 201, it iseffective to make the film thickness of the active layer (especially thechannel forming region) thin (preferably from 20 to 50 nm, morepreferably between 25 and 40 nm).

Next, reference numeral 41 denotes a first passivation film, and itsfilm thickness may be set from 10 nm to 1 μm (preferably between 200 and500 nm). An insulating film containing silicon (in particular,preferably a silicon nitride oxide film or a silicon nitride film) canbe used as the passivation film material. The passivation film 41 playsthe role of protecting the manufactured TFT from contaminant matter andmoisture. Alkaline metals such as sodium are contained in an EL layerformed on the final TFT. In other words, the first passivation film 41works as a protecting layer so that these alkaline metals (mobile ions)do not penetrate into the TFT. Note that alkaline metals andalkaline-earth metals are contained in the term ‘alkaline metal’throughout this specification.

Further, by making the passivation film 41 possess a heat radiationeffect, it is also effective in preventing thermal degradation of the ELlayer. Note that light is emitted from the base 11 side in the FIG. 1structure of the EL display device, and therefore it is necessary forthe passivation film 41 to have light transmitting characteristics. Inaddition, in case of using an organic material for the EL layer, itdeteriorates by bonding with oxygen so it if preferable not to use aninsulating film that easily releases oxygen.

An insulating film containing at least one element selected from thegroup consisting of B (boron), C (carbon), and N (nitrogen), and atleast one element selected from the group consisting of Al (aluminum),Si (silicon), and P (phosphorous) can be given as a light transparentmaterial that prevents penetration of alkali metals and also possessheat radiation qualities. For example, it is possible to use: analuminum nitride compound, typically aluminum nitride (Al_(x)N_(y)); asilicon carbide compound, typically silicon carbide (Si_(x)C_(y)); asilicon nitride compound, typically silicon nitride (Si_(x)N_(y)); aboron nitride compound, typically boron nitride (B_(x)N_(y)); or a boronphosphate compound, typically boron phosphate (B_(x)P_(y)). Further, analuminum oxide compound, typically aluminum oxide (Al_(x)O_(y)), hassuperior light transparency characteristics, and has a thermalconductivity of 20 Wm⁻¹K⁻¹, and can be said to be a preferable material.These materials not only possess heat radiation qualities, but also areeffective in preventing the penetration of substances such as moistureand alkaline metals. Note that x and y are arbitrary integers for theabove transparent materials.

The above chemical compounds can also be combined with another element.For example, it is possible to use nitrated aluminum oxide, denoted byAlN_(x)O_(y), in which nitrogen is added to aluminum oxide. Thismaterial also not only possesses heat radiation qualities, but also iseffective in preventing the penetration of substances such as moistureand alkaline metals. Note that x and y are arbitrary integers for theabove nitrated aluminum oxide.

Furthermore, the materials recorded in Japanese Patent ApplicationLaid-open No. Sho 62-90260 can also be used. Namely, a chemical compoundcontaining Si, Al, N, O, and M can also be used (note that M is arare-earth element, preferably an element selected from the groupconsisting of Ce (cesium), Yb (ytterbium), Sm (samarium), Er (erbium), Y(yttrium), La (lanthanum), Gd (gadolinium), Dy (dysprosium), and Nd(neodymium)). These materials not only possess heat radiation qualities,but also are effective in preventing the penetration of substances suchas moisture and alkaline metals.

Furthermore, carbon films such as a diamond thin film or amorphouscarbons (especially those which have characteristics close to those ofdiamond; referred to as diamond-like carbon) can also be used. Thesehave very high thermal conductivities, and are extremely effective asradiation layers. Note that if the film thickness becomes larger, thereis brown banding and the transmissivity is reduced, and therefore it ispreferable to use as thin a film thickness (preferably between 5 and 100nm) as possible.

Note that the aim of the first passivation film 41 is in protecting theTFT from alkaline metals and from moisture, and therefore it must madeso as to not lose this effect. A thin film made from a materialpossessing the above radiation effect can be used by itself, but it iseffective to laminate this thin film and an insulating film that iscapable of preventing penetration of alkaline metals and moisture(typically a silicon nitride film (Si_(x)N_(y)) or a silicon nitrideoxide film (SiO_(x)N_(y))). Note that x and y are arbitrary integers forthe above silicon nitride films and silicon nitride oxide films.

Note that EL display devices are roughly divided into four types ofcolor displays: a method of forming three types of EL elementscorresponding to R, G, and B; a method of combining white colorluminescing EL elements with color filters; a method of combining blueor blue-green luminescing EL elements and fluorescent matter(fluorescing color change layer, CCM); and a method of using atransparent electrode as a cathode (opposing electrode) and overlappingEL elements corresponding to R, G, and B.

The structure of FIG. 1 is an example of a case of using a method inwhich 3 kinds of EL layers are formed corresponding to R, G and B. Notethat though one pixel is shown in FIG. 1, pixels of the same structureare formed in correspondence to the each color of red, green or blue,and accordingly color display can be performed. Known materials may beadopted for the EL layers of the respective colors.

Note that it is possible to implement the present invention withoutbeing concerned with the method of luminescence, and that all four ofthe above methods can be used with the present invention.

Further, after forming the first passivation film 41, a secondinterlayer insulating film (it may also be referred to as a flatteningfilm) 44 is formed to cover each TFT, and leveling of step due to TFTsis performed. A resin film is preferable for the second interlayerinsulating film 44 and it is good if polyimide, polyamide, acrylic, BCB(benzocyclobutene), etc., is used. Needless to say, an inorganic filmmay be used if a sufficient leveling is possible.

The leveling of steps due to the TFT by the second interlayer insulatingfilm 44 is extremely important. The EL layer formed afterward is verythin, and therefore there are cases in which poor luminescence is causedby the existence of a step. It is therefore preferable to performleveling before forming a pixel electrode so as to be able to form theEL layer on as level a surface as possible.

Further, reference numeral 45 is a second passivation film, and plays animportant role of blocking alkaline metals diffused from the ELelements. A film thickness may be from 5 nm to 1 μm (typically between20 and 300 nm). An insulating film capable of preventing penetration ofalkaline metals is used as the second passivation film 45. Materialsused for the first passivation film 41 can be used as the material.

Furthermore, this second passivation film 45 functions as a radiatinglayer that function to release heat generated on EL elements so as notto store heat on the El elements. In addition, in case that the secondinterlayer insulating film 44 is a resin film it is weak against heat,so the measures are taken that the heat generated by EL elements notgive bad influence on the second interlayer insulating film 44.

It is effective to perform leveling of the TFT by the resin film inmanufacturing the EL display device, as stated above, but there has notbeen a conventional structure which considers the deterioration of theresin film due to heat generated by the EL element. It can be said thatone of the characteristics of the present invention is to solve thatpoint by disposing the second passivation film 45.

Further, the second passivation film 45 prevents the above stateddegradation due to heat, and at the same time it can also function as aprotecting layer in order that alkaline metals within the EL layer donot diffuse toward the TFT, and in addition it also functions as aprotecting layer so that moisture and oxygen do not penetrate into theEL layer from the TFT.

The point that TFT side and EL element side are segregated by aninsulating film that has high radiating effect and that is capable ofpreventing penetration of moisture and alkaline metals, is one of theimportant characteristics of the present invention and it can be saidthat it is a structure which does not exist in a conventional EL displaydevice.

Reference numeral 46 denotes a pixel electrode (EL element anode) madefrom a transparent conducting film and it is formed so as to beconnected to the drain wiring 37 of the current control TFT 202 in anopening section after opening a contact hole in the second passivationfilm 45, in second interlayer insulating film 44 and in the firstpassivation film 41.

After the pixel electrode 46 is formed, banks 101 a and 101 b comprisinga resin film are formed on the second passivation film 45. A photosensitive polyimide film is formed by spin coating in the presentembodiment mode and banks 101 a and 101 b are formed by patterning.These banks 101 a and 101 b are grooves in forming EL layers by ink jetmethod, and the position where EL elements are formed are determined bythe disposition of these banks.

After banks 101 a and 101 b are formed, an EL layer 47 is next formed(an organic material is preferable). The EL layer may be used by asingle layer by a laminate structure, but there are more cases in whichlaminate structure is used. Though various laminate structures aresuggested by combining an emitting layer, an electron transportinglayer, an electron injecting layer, a hole injecting layer or a holetransporting layer, any structure is acceptable in the presentinvention. Further, a fluorescent dye, etc. may be doped in the ELlayer.

All already known EL materials can be used by the present invention.Organic materials are widely known as such materials, and consideringthe driver voltage, it is preferable to use an organic material. Forexample, the materials disclosed in the following U.S. patents andJapanese patent applications can be used as the organic EL material:

U.S. Pat. No. 4,356,429; U.S. Pat. No. 4,539,507; U.S. Pat. No.4,720,432; U.S. Pat. No. 4,769,292; U.S. Pat. No. 4,885,211; U.S. Pat.No. 4,950,950; U.S. Pat. No. 5,059,861; U.S. Pat. No. 5,047,687; U.S.Pat. No. 5,073,446; U.S. Pat. No. 5,059,862; U.S. Pat. No. 5,061,617;U.S. Pat. No. 5,151,629; U.S. Pat. No. 5,294,869; U.S. Pat. No.5,294,870; Japanese Patent Application Laid-open No. Hei 10-189525;Japanese Patent Application Laid-open No. Hei 8-241048; and JapanesePatent Application Laid-open No. Hei 8-78159, the disclosures of whichare herein incorporated by reference.

Specifically, an organic material such as the one shown by the followinggeneral formula can be used as a hole injecting layer.

[Chem 1]

Here, Q is either N or a C—R (carbon chain); M is a metal, a metaloxide, or a metal halide; R is hydrogen, an alkyl, an aralkyl, an aryl,or an alkalyl; and T1 and T2 are unsaturated six member rings includingsubstituent such as hydrogen, alkyl, or halogen.

Furthermore, an aromatic tertiary amine can be used as an organicmaterial hole transporting layer, preferably including thetetraaryldiamine shown by the following general formula.

[Chem 2]

In Chem 2 Are is an arylene group, n is an integer from 1 to 4, and Ar,R₇, R₈, and R₉ are each various chosen aryl groups.

In addition, a metal oxynoid compound can be used as an organic materialEL layer, electron transporting layer, or electron injecting layer. Amaterial such as that shown by the general formula below may be used asthe metal oxinoid compound.

[Chem 3]

It is possible to substitute R₂ through R₇, and a metal oxinoid such asthe following can also be used.

[Chem 4]

In Chem 4, R₂ through R₇ are defined as stated above; L₁ through L₅ arecarbohydrate groups containing from 1 to 12 carbon elements; and both L₁and L₂, or both L₂ and L₃ are formed by benzo-rings. Further, a metaloxinoid such as the following may also be used.

[Chem 5]

It is possible to substitute R₂ through R₆ here. Coordination compoundshaving organic ligands are thus included as organic EL materials. Notethat the above examples are only some examples of organic EL materialswhich can be used as the EL material of the present invention, and thatthere is absolutely no need to limit the EL material to these.

In the present invention, since an ink-jet method is used as a formingmethod of an EL layer, many polymer materials can be used as preferableEL materials. As typical polymer materials, polymer materials, such aspolyparaphenylene vinylene (PPV), polyfluorene, or polyvinylcarbazole(PVK), can be enumerated. For colorization, it is preferable to use, forexample, cyanopolyphenylene vinylene as a red light emitting material,to use polyphenylene vinylene as a green light emitting material, and touse polyphenylene vinylene and polyalkylphenylene as a blue lightemitting material.

Incidentally, there are various types as PPV organic EL materials, and amolecular formula as set forth below is reported for example (H. Shenk,H. Becker, O. Gelsen, E. Kluge, E. Kreuder, and H. Spreitzer, EuroDisplay, Proceedings, 1999, p. 33-37, “Polymers for Light EmittingDiodes”).

[Chem 6]

[Chem 7]

It is also possible to use polyphenylvinyl having a molecular formuladisclosed in Japanese Patent Application Laid-open No. Hei 10-92576. Themolecular formula is as follows:

[Chem 8]

[Chem 9]

As a PVK organic EL material, there is a molecular formula as follows:

[Chem 10]

A polymer organic EL material may be applied after it is dissolved in asolvent while it is in a polymer state, or it may be polymerized afterit is dissolved in a solvent while it is in a monomer state andapplication thereof is made. In the case where application is made in amonomer state, a polymer precursor is first formed, and is polymerizedby heating in vacuum so that it becomes a polymer.

As a specific light emitting layer, it is appropriate thatcyanopolyphenylene vinylene is used for a light emitting layer radiatingred light, polyphenylene vinylene is used for a light emitting layerradiating green light, and polyphenylene vinylene or polyalkylphenyleneis used for a light emitting layer radiating blue light. It isappropriate that its film thickness is made 30 to 150 nm (preferably 40to 100 nm).

As a typical solvent, toluene, xylene, cymene, chloroform,dichloromethane, γ-butyl lactone, butyl cellosolve, and NMP(N-methyl-2-pyrolidone) are enumerated. It is also effective to add anadditive to raise viscosity of an applied solution.

However, the foregoing examples are merely examples of organic ELmaterials, which can be used for EL materials of the present invention,and it is absolutely unnecessary to limit the invention to these. Withrespect to organic EL materials, which can be used for an ink-jetmethod, all materials disclosed in Japanese Patent Application Laid-openNo. Hei 10-012377 can be cited.

Incidentally, although the ink-jet method is roughly classified into abubble-jet method (also called a thermal ink-jet method) and a piezomethod, in order to carry out the present invention, the piezo method ispreferable. The difference between the two will be described withreference to FIGS. 19A and 19B.

FIG. 19A shows an example of the piezo method, and reference numeral1901 designates a piezo element (piezoelectric element); 1902, a metalpipe; and 1903, a mixture solution of an ink material and an EL material(hereinafter referred to as an EL forming solution). When a voltage isapplied, the piezo element is deformed, and the metal pipe 1902 is alsodeformed. As a result, the inside EL forming solution 1903 is ejected asa droplet 1904. Like this, by controlling the voltage applied to thepiezo element, application of the EL forming solution is carried out. Inthis case, since the EL forming solution 1903 is pushed out by aphysical external pressure, its composition etc. is not influenced atall.

FIG. 19B shows an example of the bubble-jet method, and referencenumeral 1905 designates a heating element; 1906, a metal pipe; and 1907,an EL forming solution. When an electric current is made to flow, theheating element 1905 generates heat, and a bubble 1908 is produced inthe EL forming solution 1907. As a result, the EL forming solution 1907is pushed out by the bubble, and is ejected as a droplet 1909. Likethis, by controlling the electric current to the heating element,application of the EL forming solution is carried out. In this case,since the EL forming solution 1907 is heated by the heating element,there is a possibility that a bad influence is exerted according to thecomposition of the EL material.

When the EL material is applied and is formed on a device by actuallyusing the ink-jet method, an EL layer is formed in the form as shown inFIG. 20. In FIG. 20, reference numeral 91 designates a pixel portion;and 92 and 93, driving circuits. A plurality of pixel electrodes 94 areformed in the pixel portion 91. Although not shown, each of the pixelelectrodes is connected to a current controlling TFT. Actually, althougha bank (see FIG. 1) for separating the pixel electrodes 94 respectivelyis provided, it is not shown here.

By the ink-jet method, a red light emitting EL layer 95, a green lightemitting EL layer 96, and a blue light emitting EL layer 97 are formed.At this time, after all the red light emitting EL layers 95 are firstformed, the green light emitting EL layers 96 and the blue lightemitting EL layers 97 may be sequentially formed. In order to remove thesolvent contained in the EL forming solution, a baking (firing)treatment is required. This baking treatment may be carried out afterall the EL layers are formed, or may be separately carried out at thepoint of time when the formation of the respective color EL layers isfinished.

When forming the EL layer, a pixel (pixel corresponding to red) wherethe red light emitting EL layer 95 is formed, a pixel (pixelcorresponding to green) where the green light emitting EL layer 96 isformed, and a pixel (pixel corresponding to blue) where the blue lightemitting EL layer 97 is formed, are made to have such a state that therespective colors are always in contact with each other as shown in FIG.20.

Such arrangement is what is called delta arrangement, and is effectivein making excellent color display. Since the merit of the ink-jet methodis in the point that the EL layers of the respective colors can be madedotted ones, it can be said that to use it for an EL display devicehaving a pixel portion of delta arrangement is the best mode.

On forming an EL layer 47, it is preferable that a treatment atmosphereis made a dry atmosphere having the least possible water and theformation is carried out in an inert gas. Since the EL layer is easilydeteriorated by the existence of water or oxygen, it is necessary toremove such a factor to the utmost when the layer is formed. Forexample, a dry nitrogen atmosphere, a dry argon atmosphere, or the likeis preferable.

When the EL layer 47 is formed by the ink-jet method in the manner asdescribed above, a cathode 48 and a protective electrode 49 are nextformed. In the present specification, alight emitting element formed ofa pixel electrode (anode), an EL layer, and a cathode is called an ELelement.

As the cathode 48, a material having a low work function and containingmagnesium (Mg), lithium (Li), cesium (Cs), barium (Ba), potassium (K),beryllium (Be), or calcium (ca) is used. Preferably, an electrode madeof MgAg (material of Mg and Al mixed at a ratio of Mg:Ag=10:1) may beused. In addition, a MgAgAl electrode, a LiAl electrode, and a LiFAlelectrode can be enumerated. The protective electrode 49 is anelectrode, which is provided to protect the cathode 48 from outsidemoisture or the like, and a material containing aluminum (Al) or silver(Ag) is used. This protective electrode 49 has also a heat radiationeffect.

Incidentally, it is preferable that the EL layer 47 and the cathode 48are continuously formed in a dry inert gas atmosphere without opening tothe air. In the case where an organic material is used for the EL layer,since it is very weak to moisture, this way is adopted to avoid moistureadsorption at the time of exposing to the air. Further, it is morepreferable to continuously form not only the EL layer 47 and the cathode48 but also the protective electrode 49 thereon.

Reference numeral 50 designates a third passivation film, and it isappropriate that its film thickness is made 10 nm to 1 μm (preferably200 to 500 nm). Although a main object of providing the thirdpassivation film 50 is to protect the EL layer 47 from moisture, a heatradiation effect may also be provided, similarly to the secondpassivation film 45. Thus, as a forming material, a similar to that ofthe first passivation film 41 can be used. However, in the case where anorganic material is used for the EL layer 47, since there is apossibility that the layer is deteriorated through combination withoxygen, it is desirable not to use an insulating film, which is apt togive off oxygen.

Besides, as described above, since the EL layer is weak to heat, it ispreferable to form a film at the lowest possible temperature (preferablyin a temperature range of from room temperature to 120° C.). Thus, itcan be said that plasma CVD, sputtering, vacuum evaporation, ionplating, or a solution application (spin coating) is a preferable filmforming method.

Like this, although the deterioration of the EL element can besufficiently suppressed by merely providing the second passivation film45, preferably, the EL element is surrounded by two-layer insulatingfilms formed to be put at both sides of the EL element, such as thesecond passivation film 45 and the third passivation film 50, so thatintrusion of moisture and oxygen into the EL layer is prevented,diffusion of alkaline metal from the EL layer is prevented, and storageof heat into the EL layer is prevented. As a result, deterioration ofthe EL layer is further suppressed, and an EL display device having highreliability can be obtained.

The EL display device of the present invention includes a pixel portionmade of a pixel having a structure as in FIG. 1, and TFTs havingdifferent structures according to functions are disposed in the pixel.By this, it is possible to form a switching TFT having a sufficientlylow off current value and a current controlling TFT strong against hotcarrier injection in the same pixel, and it is possible to obtain the ELdisplay device having high reliability and enabling excellent picturedisplay (having high operation performance).

Incidentally, in the pixel structure of FIG. 1, although a TFT having amulti-gate structure is used as the switching TFT, it is not necessaryto limit a structure of arrangement of LDD regions or the like to thestructure of FIG. 1.

The present invention made of the foregoing structure will be describedin more detail with reference to embodiments described below.

Embodiment 1

The embodiments of the present invention are explained using FIGS. 3A to5C. A method of manufacturing a pixel portion, and TFTs of a drivercircuit portion formed in the periphery of the pixel portion, isexplained here. Note that in order to simplify the explanation, a CMOScircuit is shown as a basic circuit for the driver circuits.

First, as shown in FIG. 3A, a base film 301 is formed with a 300 nmthickness on a glass substrate 300. Silicon nitride oxide films arelaminated as the base film 301 in embodiment 1. It is good to set thenitrogen concentration to between 10 and 25 wt % in the film contactingthe glass substrate 300.

Further, it is effective to form an insulating film made from the samematerial as that of the first passivation film 41 shown in FIG. 1, as aportion of the base film 301. A large electric current flows in acurrent control TFT, heat is easily generated, and therefore it iseffective to form an insulating film that has a heat radiating effect asclose as possible to the current control TFT.

Next, an amorphous silicon film (not shown in the figures) is formedwith a thickness of 50 nm on the base film 301 by a known depositionmethod. Note that it is not necessary to limit this to the amorphoussilicon film, and another film may be formed provided that it is asemiconductor film containing an amorphous structure (including amicrocrystalline semiconductor film). In addition, a compoundsemiconductor film containing an amorphous structure, such as anamorphous silicon germanium film, may also be used. Further, the filmthickness may be made from 20 to 100 nm.

The amorphous silicon film is then crystallized by a known method,forming a crystalline silicon film (also referred to as apolycrystalline silicon film or a polysilicon film) 302. Thermalcrystallization using an electric furnace, laser annealingcrystallization using a laser, and lamp annealing crystallization usingan infrared lamp exist as known crystallization methods. Crystallizationis performed in embodiment 1 using light from an excimer laser whichuses XeCl gas.

Note that pulse emission type excimer laser light formed into a linearshape is used in embodiment 1, but a rectangular shape may also be used,and continuous emission argon laser light and continuous emissionexcimer laser light can also be used.

The crystalline silicon film is used as an active layer of the TFTs inembodiment 1, but it is also possible to use an amorphous silicon filmas the active layer. However, it is necessary for a large current toflow through the current control TFT, and therefore it is moreadvantageous to use the crystalline silicon film, through which currenteasily flows.

Note that it is effective to form the active layer of the switching TFT,in which there is a necessity to reduce the off current, by theamorphous silicon film, and to form the active layer of the currentcontrol TFT by the crystalline silicon film. Electric current flows withdifficulty in the amorphous silicon film because the carrier mobility islow, and the off current does not easily flow. In other words, the mostcan be made of the advantages of both the amorphous silicon film,through which current does not flow easily, and the crystalline siliconfilm, through which current easily flows.

Next, as shown in FIG. 3B, a protecting film 303 is formed on thecrystalline silicon film 302 from a silicon oxide film having athickness of 130 nm. This thickness may be chosen within the range of100 to 200 nm (preferably between 130 and 170 nm). Furthermore, otherfilms may also be used providing that they are insulating filmscontaining silicon. The protecting film 303 is formed so that thecrystalline silicon film is not directly exposed to plasma duringaddition of an impurity, and so that it is possible to have delicateconcentration control of the impurity.

Resist masks 304 a and 304 b are then formed on the protecting film 303,and an impurity element which imparts n-type conductivity (hereafterreferred to as an n-type impurity element) is added. Note that elementsresiding in periodic table group 15 are generally used as the n-typeimpurity element, and typically phosphorous or arsenic can be used. Notethat a plasma doping method is used, in which phosphine (PH₃) is plasmaactivated without separation of mass, and phosphorous is added at aconcentration of 1×10¹⁸ atoms/cm³ in embodiment 1. An ion implantationmethod, in which separation of mass is performed, may also be used, ofcourse.

The dose amount is regulated so that the n-type impurity element iscontained in n-type impurity regions 305 and 306, thus formed by thisprocess, at a concentration of 2×10¹⁶ to 5×10¹⁹ atoms/cm³ (typicallybetween 5×10¹⁷ and 5×10⁸ atoms/cm³).

Next, as shown in FIG. 3C, the protecting film 303 is removed, andactivation of the added periodic table group 15 element is performed. Aknown technique of activation may be used as the means of activation,and activation is done in embodiment 1 by irradiation of excimer laserlight. Both of pulse emission type laser and a continuous emission typelaser may be used, and it is not necessary to place any limits on theuse of excimer laser light. The goal is the activation of the addedimpurity element, and it is preferable that irradiation is performed atan energy level at which the crystalline silicon film does not melt.Note that the laser irradiation may also be performed with theprotecting film 303 in place.

Activation by heat treatment may also be performed along with activationof the impurity element by laser light. When activation is performed byheat treatment, considering the heat resistance of the substrate, it isgood to perform heat treatment on the order of 450 to 550° C.

A boundary portion (connecting portion) with regions along the edges ofthe n-type impurity regions 305 and 306, namely regions along theperimeter into which the n-type impurity element, which exists in then-type impurity regions 305 and 306, is not added, is defined by thisprocess. This means that, at the point when the TFTs are latercompleted, extremely good connections can be formed between LDD regionsand channel forming regions.

Unnecessary portions of the crystalline silicon film are removed next,as shown in FIG. 3D, and island shape semiconductor films (hereafterreferred to as active layers) 307 to 310 are formed.

Then, as shown in FIG. 3E, a gate insulating film 311 is formed,covering the active layers 307 to 310. An insulating film containingsilicon and with a thickness of 10 to 200 nm, preferably between 50 and150 nm, may be used as the gate insulating film 311. A single layerstructure or a lamination structure may be used. A 110 nm thick siliconnitride oxide film is used in embodiment 1.

A conducting film with a thickness of 200 to 400 nm is formed next andpatterned, forming gate electrodes 312 to 316. Note that in embodiment1, the gate electrodes and lead wirings electrically connected to thegate electrodes (hereafter referred to as gate wirings) are formed fromdifferent materials. Specifically, a material having a lower resistancethan that of the gate electrodes is used for the gate wirings. This isbecause a material which is capable of being micro-processed is used asthe gate electrodes, and even if the gate wirings cannot bemicro-processed, the material used for the wirings has low resistance.Of course, the gate electrodes and the gate wirings may also be formedfrom the same material.

Further, the gate wirings may be formed by a single layer conductingfilm, and when necessary, it is preferable to use a two layer or a threelayer lamination film. All known conducting films can be used as thegate electrode material. However, as stated above, it is preferable touse a material which is capable of being micro-processed, specifically,a material which is capable of being patterned to a line width of 2 μmor less.

Typically, a film of a material chosen from among the group consistingof tantalum (Ta), titanium (Ti), molybdenum (Mo), tungsten (W), andchromium (Cr); or a nitrated compound of the above elements (typically atantalum nitride film, a tungsten nitride film, or a titanium nitridefilm); or an alloy film of a combination of the above elements(typically a Mo—W alloy or a Mo—Ta alloy); or a silicide film of theabove elements (typically a tungsten silicide film or a titaniumsilicide film); or a silicon film which has been made to possessconductivity can be used. A single layer film or a lamination may beused, of course.

A lamination film made from a 50 nm thick tantalum nitride (TaN) filmand a 350 nm thick Ta film is used in embodiment 1. It is good to formthis film by sputtering. Furthermore, if an inert gas such as Xe or Neis added as a sputtering gas, then film peeling due to the stress can beprevented.

The gate electrodes 313 and 316 are formed at this time so as to overlapa portion of the n-type impurity regions 305 and 306, respectively,sandwiching the gate insulating film 311. This overlapping portion laterbecomes an LDD region overlapping the gate electrode.

Next, an n-type impurity element (phosphorous is used in embodiment 1)is added in a self-aligning manner with the gate electrodes 312 to 316as masks, as shown in FIG. 4A. The addition is regulated so thatphosphorous is added to impurity regions 317 to 323 thus formed at aconcentration of 1/10 to ½ that of the impurity regions 305 and 306(typically between ¼ and ⅓). Specifically, a concentration of 1×10¹⁶ to5×10¹⁸ atoms/cm³(typically 3×10¹⁷ to 3×10¹⁸ atoms/cm³) is preferable.

Resist masks 324 a to 324 d are formed next to cover the gateelectrodes, as shown in FIG. 4B, and an n-type impurity element(phosphorous is used in embodiment 1) is added, forming impurity regions325 to 331 containing a high concentration of phosphorous. Ion dopingusing phosphine (PH₃) is also performed here, and is regulated so thatthe phosphorous concentration of these regions is from 1×10²⁰ to 1×10²¹atoms/cm³ (typically between 2×10²⁰ and 5×10²⁰ atoms/cm³).

A source region or a drain region of the n-channel TFT is formed by thisprocess, and in the switching TFT, a portion of the n-type impurityregions 320 to 322 formed by the process of FIG. 4A remains. Theseremaining regions correspond to the LDD regions 15 a to 15 d of theswitching TFT in FIG. 1.

Next, as shown in FIG. 4C, the resist masks 324 a to 324 d are removed,and a new resist mask 332 is formed. A p-type impurity element (boron isused in embodiment 1) is then added, forming impurity regions 333 and334 containing a high concentration of boron. Boron is added here to aconcentration of 3×10²⁰ to 3×10²¹ atoms/cm³ (typically between 5×10²⁰and 1×10²¹ atoms/cm³) by ion doping using diborane (B₂H₆).

Note that phosphorous has already been added to the impurity regions 333and 334 at a concentration of 1×10¹⁶ to 5×10¹⁸ atoms/cm³, but boron isadded here at a concentration of at least 3 times that of thephosphorous. Therefore, the n-type impurity regions already formedcompletely invert to p-type, and function as p-type impurity regions.

Next, after removing the resist mask 332, the n-type and p-type impurityelements added at various concentrations are activated. Furnaceannealing, laser annealing, or lamp annealing may be performed as ameans of activation. Heat treatment is performed in embodiment 1 in anitrogen atmosphere for 4 hours at 550° C. in an electric furnace.

It is important to remove as much of the oxygen in the atmosphere aspossible at this time. This is because if any oxygen exists, then theexposed surface of the electrode oxidizes, inviting an increase inresistance, and at the same time it becomes more difficult to later makean ohmic contact. It is therefore preferable that the concentration ofoxygen in the atmosphere in the above activation process be 1 ppm orless, desirably 0.1 ppm or less.

After the activation process is completed, a gate wiring 335 with athickness of 300 nm is formed next. A metallic film having aluminum (Al)or copper (Cu) as its principal constituent (comprising 50 to 100% ofthe composition) may be used as the material of the gate wiring 335. Aswith the gate wiring 211 of FIG. 2, the gate wiring 335 is formed with aplacement so that the gate electrodes 314 and 315 of the switching TFTs(corresponding to gate electrodes 19 a and 19 b of FIG. 2) areelectrically connected. (See FIG. 4D.)

The wiring resistance of the gate wiring can be made extremely small byusing this type of structure, and therefore a pixel display region(pixel portion) having a large surface area can be formed. Namely, thepixel structure of embodiment 1 is extremely effective because an ELdisplay device having a screen size of a 10 inch diagonal or larger (inaddition, a 30 inch or larger diagonal) is realized.

A first interlayer insulating film 336 is formed next, as shown in FIG.5A. A single layer insulating film containing silicon is used as thefirst interlayer insulating film 336, but a lamination film may becombined in between. Further, a film thickness of between 400 nm and 1.5μm may be used. A lamination structure of an 800 nm thick silicon oxidefilm on a 200 nm thick silicon nitride oxide film is used in embodiment1.

In addition, heat treatment is performed for 1 to 12 hours at 300 to450° C. in an atmosphere containing between 3 and 100% hydrogen,performing hydrogenation. This process is one of hydrogen termination ofdangling bonds in the semiconductor film by hydrogen which is thermallyactivated. Plasma hydrogenation (using hydrogen activated by a plasma)may also be performed as another means of hydrogenation.

Note that the hydrogenation step may also be inserted during theformation of the first interlayer insulating film 336. Namely, hydrogenprocessing may be performed as above after forming the 200 nm thicksilicon nitride oxide film, and then the remaining 800 nm thicksilicon-oxide film may be formed.

A contact hole is formed next in the first interlayer insulating film336, and source wirings 337 to 340, and drain wirings 341 to 343 areformed. In embodiment 1, a lamination film with a three layeredstructure of a 100 nm titanium film, a 300 nm aluminum film containingtitanium, and a 150 nm titanium film, formed successively by sputtering,is used as these wirings. Other conducting films may also be used, ofcourse, and an alloy film containing silver, palladium, and copper mayalso be used.

A first passivation film 344 is formed next with a thickness of 50 to500 nm (typically between 200 and 300 nm). A 300 nm thick siliconnitride oxide film is used as the first passivation film 344 inembodiment 1. This may also be substituted by a silicon nitride film. Itis of course possible to use the same materials as those of the firstpassivation film 41 of FIG. 1.

Note that it is effective to perform plasma processing using a gascontaining hydrogen such as H₂ or NH₃ before the formation of thesilicon nitride oxide film. Hydrogen activated by this preprocess issupplied to the first interlayer insulating film 336, and the filmquality of the first passivation film 344 is improved by performing heattreatment. At the same time, the hydrogen added to the first interlayerinsulating film 336 diffuses to the lower side, and the active layerscan be hydrogenated-effectively.

A second interlayer insulating film 347 is formed next from an organicresin. Materials such as polyimide, polyamide, acrylic, and BCB(benzocyclobutene) can be used as the organic resin. In particular, thepurpose of being a leveling film is strong in the second interlayerinsulating film 347, and therefore acrylic, having superior levelingcharacteristics, is preferable. An acrylic film is formed in embodiment1 with a film thickness which can sufficiently level the step due toTFTs. This thickness is preferably from 1 to 5 μm (more preferablybetween 2 and 4 μm).

Next, a second passivation film 348 having a thickness of 100 nm isformed on the second interlayer insulating film 347. In this embodiment,since an insulating film containing Si, Al, N, O and La is used, it ispossible to prevent alkaline metal from diffusing from the EL layerprovided thereon. At the same time, intrusion of moisture into the ELlayer is blocked and heat generated in the EL layer is dissipated, sothat it is possible to suppress deterioration of the EL layer due toheat and deterioration of the flattened film (second interlayerinsulating film).

Then, a contact hole reaching the drain wiring line 343 is formedthrough the second passivation film 348, the second interlayerinsulating film 347, and the first passivation film 344, and a pixelelectrode 349 is formed. In this embodiment, a compound film of indiumoxide and tin oxide (ITO) is formed to a thickness of 110 nm, andpatterning is carried out to make the pixel electrode. This pixelelectrode 349 becomes an anode of the EL element. As other materials, itis also possible to use a compound film of indium oxide and zinc oxideor a zinc oxide film containing gallium oxide.

Incidentally, this embodiment has such a structure that the pixelelectrode 349 is electrically connected to the drain region 331 of thecurrent controlling TFT through the drain wiring line 343. Thisstructure has merits as follows:

Since the pixel electrode 349 comes in direct contact with an organicmaterial of an EL layer (light emitting layer) or charge transportinglayer, there is a possibility that a movable ion contained in the ELlayer or the like diffuses in the pixel electrode. That is, in thestructure of this embodiment, the pixel electrode 349 is not directlyconnected to the drain region 331 which is a part of the active layer,but the wiring line 343 is made to intervene so that penetration of themovable ion into the active layer can be prevented.

Next, as shown in FIG. 5C, an EL layer 350 is formed by the ink-jetmethod, and further, a cathode (MgAg electrode) 351 and a protectionelectrode 352 are formed without exposure to the air. At this time, itis preferable that prior to formation of the EL layer 350 and thecathode 351, a heat treatment is carried out to the pixel electrode 349to completely remove moisture. Incidentally, in this embodiment,although the MgAg electrode is used as the cathode of the EL element,another well-known material may be used.

Incidentally, for the EL layer 350, it is possible to use materialsdescribed before. In this embodiment, as shown in FIG. 21, a four-layerstructure of a hole injecting layer 5002, a hole transporting layer5003, an emitting layer 5004, and an electron transporting layer 5005forms the EL layer. However, there is also a case where the electrontransporting layer is not provided, or there is also a case where anelectron injecting layer is provided. Besides, there is also a casewhere the hole injecting layer is omitted. Like this, various examplesof combination have already been reported, and any structure of them maybe used. Further, in FIG. 21, reference numeral 5001 indicates an anodeand 5006 indicates a cathode.

As the hole injecting layer or hole transporting layer, it isappropriate that amine TPD (triphenylamines) is used, and in addition,hydrazone (typically DEH), stilbene (typically STB), starburst(typically m-MTDATA) or the like may be used. Especially, a starburstmaterial having high glass transition temperature and hard tocrystallize is preferable. Besides, polyaniline (PAni), polythiophene(PEDOT), or copper phthalocyanine (CuPc) may be used.

Besides, as the light emitting layer used in this embodiment, it isappropriate that cyanopolyphenylene vinylene is used for a lightemitting layer radiating red light, polyphenylene vinylene is used for alight emitting layer radiating green light, and polyphenylene vinyleneor polyalkylphenylene is used for a light emitting layer radiating bluelight. It is appropriate that its film thickness is made 30 to 150 nm(preferably 40 to 100 nm). Besides, in this embodiment, toluene is usedas the solvent.

Although even the protective electrode 352 can protect the EL layer 350from moisture or oxygen, more preferably, a third passivation film 353may be provided. In this embodiment, as the third passivation film 353,a silicon nitride film having a thickness of 300 nm is provided. Thisthird passivation film may also be formed continuously after theprotective electrode 352 without exposure to the air. Of course, as thethird passivation film 353, the same material as the third passivationfilm 50 of FIG. 1 may be used.

Besides, the protective electrode 352 is provided to preventdeterioration of the MgAg electrode 351, and a metal film containingaluminum as its main ingredient is typical. Of course, other materialsmay be used too. Since the EL layer 350 and the MgAg electrode 351 arevery weak to moisture, it is desirable to make continuous formation tothe protective electrode 352 without exposure to the air so that the ELlayer is protected from the outside air.

Incidentally, it is appropriate that the thickness of the EL layer 350is made 10 to 400 nm (typically 60 to 160 nm), and the thickness of theMgAg electrode 351 is made 180 to 300 nm (typically 200 to 250 nm). Inthe case where the EL layer 350 is made a laminate structure, it isappropriate that the thickness of each layer is made within a range of10 to 100 nm.

In this way, an active matrix type EL display device having a structureas shown in FIG. 5C is completed. In the active matrix type EL displaydevice of this embodiment, TFTs having an optimum, structure aredisposed in not only the pixel portion but also the driving circuitportion, so that very high reliability is obtained and operationcharacteristics can also be improved.

First, a TFT having a structure to reduce hot carrier injection withoutdecreasing the operation speed thereof as much as possible is used as ann-channel TFT 205 of a CMOS circuit forming a driving circuit.Incidentally, the driving circuit here includes a shift register, abuffer, a level shifter, a sampling circuit (transfer gate) and thelike. In the case where digital driving is made, a signal conversioncircuit such as a D/A converter can also be included.

In the case of this embodiment, as shown in FIG. 5C, the active layer ofthe n-channel TFT 205 includes a source region 355, a drain region 356,an LDD region 357 and a channel forming region 358, and the LDD region357 overlaps with the gate electrode 313, by interposing the gateinsulating film 311 therebetween.

Consideration not to drop the operation speed is the reason why the LDDregion is formed at only the drain region side. In this n-channel TFT205, it is not necessary to pay attention to an off current value verymuch, rather, it is better to give importance to an operation speed.Thus, it is desirable that the LDD region 357 is made to completelyoverlap with the gate electrode to decrease a resistance component to aminimum. That is, it is preferable to remove the so-called offset.

In the p-channel TFT 206 of the CMOS circuit, since deterioration due tohot carrier injection can be almost neglected, an LDD region does nothave to be particularly provided. Of course, similarly to the n-channelTFT 205, it is also possible to provide an LDD region to take acountermeasure against hot carriers.

Incidentally, a sampling circuit among driving circuits is ratherspecific as compared with other circuits, and a large current flowsthrough a channel forming region in both directions. That is, the rolesof a source region and a drain region are counterchanged. Further, it isnecessary to suppress an off current value to the lowest possible value,and in that meaning, it is desirable to dispose a TFT having anapproximately intermediate function between the switching TFT and thecurrent controlling TFT.

Thus, as an n-channel TFT forming the sampling circuit, it is preferableto dispose a TFT having a structure as shown in FIG. 9. As shown in FIG.9, parts of LDD regions 901 a and 901 b overlap with a gate electrode903, putting a gate insulating film 902 therebetween. This effect is asset forth in the explanation of the current controlling TFT 202, and adifferent point is that in the sampling circuit, the LDD regions 901 aand 901 b are provided to be put at both sides of a channel formationregion 904.

Besides, a pixel having a structure as shown in FIG. 1 is formed to forma pixel portion. Since the structure of a switching TFT and a currentcontrolling TFT formed in the pixel has already been described in FIG.1, the description here is omitted.

Note that when the state of FIG. 5C is completed, it is preferable tomake packaging (sealing) by a housing member such as a protection filmhaving high airtightness (laminate film, ultraviolet ray curing resinfilm, etc.) or a ceramic sealing can so as to prevent exposure to theouter air. At that time, when the inside of the housing member is madean inert gas atmosphere, or a moisture absorbent (for example, bariumoxide) or an antioxidant is disposed in the inside, the reliability(lifetime) of the EL layer is improved.

After the airtightness is raised by processing such as packaging, aconnector (flexible print circuit: FPC) for connecting a terminalextended from the element or circuit formed on the substrate to anexternal signal terminal is attached so that a product is completed. Inthe present specification, the EL display device, which is made to havesuch a state that it can be shipped, is called an EL module.

Here, the structure of the active matrix type EL display device of thisembodiment will be described with reference to a perspective view ofFIG. 6. The active matrix type EL display device of this embodiment isconstituted by a pixel portion 602, a gate side driving circuit 603, anda source side driving circuit 604 formed on a glass substrate 601. Aswitching TFT 605 of a pixel portion is an n-channel TFT, and isdisposed at an intersection point of a gate wiring line 606 connected tothe gate side driving circuit 603 and a source wiring line 607 connectedto the source side driving circuit 604. The drain of the switching TFT605 is connected to the gate of a current controlling TFT 608.

Further, the source of the current controlling TFT 608 is connected to acurrent supply line 609, and an EL element 610 is electrically connectedto the drain of the current controlling TFT 608. At this time, if thecurrent controlling TFT 608 is an n-channel TFT, it is preferable that acathode of the EL element 610 is connected to the drain. If the currentcontrolling TFT 608 is a p-channel TFT, it is preferable that an anodeof the EL element 610 is connected to the drain.

Input wiring lines (connection wiring lines) 612 and 613 fortransmitting signals to the driving circuits and an input wiring line614 connected to the current supply line 609 are provided in an FPC 611as an external input terminal.

An example of circuit structure of the EL display device shown in FIG. 6is shown in FIG. 7. The EL display device of this embodiment includes asource side driving circuit 701, a gate side driving circuit (A) 707, agate side driving circuit (B) 711, and a pixel portion 706.Incidentally, in the present specification, the term “driving circuit”is a general term including the source side driving circuit and the gateside driving circuit.

The source side driving circuit 701 is provided with a shift register702, a level shifter 703, a buffer 704, and a sampling circuit (transfergate) 705. The gate side driving circuit (A) 707 is provided with ashift register 708, a level shifter 709, and a buffer 710. The gate sidedriving circuit (B) 711 also has the similar structure.

Here, the shift registers 702 and 708 have driving voltages of 5 to 16 V(typically 10 V) respectively, and the structure indicated by 205 inFIG. 5C is suitable for an n-channel TFT used in a CMOS circuit formingthe circuit.

Although the driving voltage of each of the level shifters 703 and 709and the buffers 704 and 710 becomes as high as 14 to 16V, similarly tothe shift register, the CMOS circuit including the n-channel TFT 205 ofFIG. 5C is suitable. Incidentally, it is effective to make a gate wiringline a multi-gate structure such as a double gate structure or a triplegate structure in improvement of reliability of each circuit.

Although the sampling circuit 705 has a driving voltage of 14 to 16 V,since the source region and drain region are inverted and it isnecessary to decrease an off current value, a CMOS circuit including then-channel TFT 208 of FIG. 9 is suitable.

The pixel portion 706 has a driving voltage of 14 to 16 V, and pixelshaving the structure shown in FIG. 1 are disposed.

The foregoing structure can be easily realized by manufacturing TFTs inaccordance with the manufacturing steps shown in FIGS. 3 to 5. In thisembodiment, although only the structure of the pixel portion and thedriving circuit are shown, if the manufacturing steps of this embodimentare used, it is possible to form a logic circuit other than the drivingcircuit, such as a signal dividing circuit, a D/A converter circuit, anoperational amplifier circuit, a γ-correction circuit, or the like onthe same substrate, and further, it is believed that a memory portion, amicroprocessor, or the like can be formed.

Further, an EL module of this embodiment including a housing member aswell will be described with reference to FIGS. 17A and 17B.Incidentally, as needed, reference numbers used in FIGS. 6 and 7 will becited. In FIG. 17B, detailed structures of TFTs in the driving circuitsand the pixel portion are omitted because those were already explained.

A pixel portion 1701, a source side driving circuit 1702, and a gateside driving circuit 1703 are formed on a substrate (including a basefilm below a TFT) 1700. Various wiring lines from the respective drivingcircuits lead to an FPC 611 through input wiring lines 612 to 614 andare connected to an external equipment.

At this time, a housing member 1704 is provided to surround at least thepixel portion, preferably the driving circuit and the pixel portion. Thehousing member 1704 has such a shape as to have a recess portion with aninner size larger than an outer size of the EL element or a sheet shape,and is fixed by an adhesive 1705 to the substrate 1700 so as to form anairtight space in cooperation with the substrate 1700. At this time, theEL element is put in such a state that it is completely sealed in theairtight space, and is completely shut off from the outer air.Incidentally, a plurality of housing members 1704 may be provided.

As a material of the housing member 1704, an insulating material such asglass or polymer is preferable. For example, amorphous glass(boro-silicate glass, quartz, etc.), crystallized glass, ceramic glass,organic resin (acrylic resin, styrene resin, polycarbonate resin, epoxyresin, etc.), and silicone resin are enumerated. Besides, ceramics maybe used. If the adhesive 1705 is an insulating material, a metalmaterial such as a stainless alloy can also be used.

As a material of the adhesive 1705, an adhesive of epoxy resin, acrylateresin, or the like can be used. Further, thermosetting resin orphoto-curing resin can also be used as the adhesive. However, it isnecessary to use such material as to block penetration of oxygen andmoisture to the utmost.

Further, it is desirable that a space 1706 between the housing memberand the substrate 1700 is filled with an inert gas (argon, helium,nitrogen, etc.). Other than the gas, an inert liquid (liquid fluorinatedcarbon typified by perfluoroalkane, etc.) can also be used. With respectto the inert liquid, a material as used in Japanese Patent ApplicationLaid-open No. Hei 8-78519 may be used. Besides, resin may be filled.

It is also effective to provide a drying agent in the space 1706. As thedrying agent, a material as disclosed in Japanese Patent ApplicationLaid-open No. Hei 9-148066 can be used. Typically, barium oxide may beused. It is also effective to provide not only the drying agent but alsoan antioxidant.

Besides, as shown in FIG. 17B, a plurality of pixels each includingisolated EL elements is provided in a pixel portion, and all of theminclude a protection electrode 1707 as a common electrode. In thisembodiment, although the description has been made such that it ispreferable to continuously form the EL layer, the cathode (MgAgelectrode) and the protective electrode without opening to the air, ifthe EL layer and the cathode are formed by using the same mask member,and only the protective electrode is formed by a different mask member,the structure of FIG. 17B can be realized.

At this time, the EL layer and the cathode may be formed on only thepixel portion, and it is not necessary to provide them on the drivingcircuit. Of course, although a problem does not arise if they areprovided on the driving circuit, when it is taken into considerationthat alkaline metal is contained in the EL layer, it is preferable notto provide.

Incidentally, the protection electrode 1707 is connected to an inputwiring line 1709 in a region indicated by 1708. The input wiring line1709 is a wiring line to give a predetermined voltage to the protectiveelectrode 1707, and is connected to the FPC 611 through a conductivepaste material (anisotropic conductive film) 1710.

Here, manufacturing steps for realizing a contact structure in theregion 1708 will be described with reference to FIG. 18.

First, in accordance with the steps of this embodiment, the state ofFIG. 5A is obtained. At this time, on the edge portion of the substrate(region indicated by 1708 in FIG. 17B), the first interlayer insulatingfilm 336 and the gate insulating film 311 are removed, and an inputwiring line 1709 is formed thereon. Of course, it is formed at the sametime as the source wiring line and the drain wiring line of FIG. 5A(FIG. 18A).

Next, in FIG. 5B, when the second passivation film 348, the secondinterlayer insulating film 347, and the first passivation film 344 areetched in FIG. 5B, a region indicated by 1801 is removed, and an openingportion 1802 is formed (FIG. 18B).

In this state, in the pixel portion, a forming step of an EL element(forming step of a pixel electrode, an EL layer and a cathode) iscarried out. At this time, in the region shown in FIG. 18, a mask memberis used so that the EL element is not formed. After a cathode 351 isformed, a protective electrode 352 is formed by using another maskmember. By this, the protective electrode 352 and the input wiring line1709 are electrically connected. Further, a third passivation film 353is provided to obtain the state of FIG. 18C.

Through the foregoing steps, the contact structure of the regionindicated by 1708 of FIG. 17B is realized. The input wiring line 1709 isconnected to the FPC 611 through a gap between the housing member 1704and the substrate 1700 (however, the gap is filled with the adhesive1705. That is, the adhesive 1705 is required to have such a thickness asto be able to sufficiently flatten unevenness due to the input wiringline). Incidentally, although the description has been made here on theinput wiring line 1709, other output wiring lines 612 to 614 are alsoconnected to the FPC 611 through the portion under the housing member1704 in the same manner.

Embodiment 2

In this embodiment, an example in which a structure of a pixel is madedifferent from the structure shown in FIG. 2B will be described withreference to FIG. 10.

In this embodiment, two pixels shown in FIG. 2B are arranged to becomesymmetrical with respect to a current supply line. That is, as shown inFIG. 10, a current supply line 213 is made common to two adjacentpixels, so that the number of necessary wiring lines can be reduced.Incidentally, a TFT structure or the like arranged in the pixel mayremain the same.

If such structure is adopted, it becomes possible to manufacture a moreminute pixel portion, and the quality of an image is improved.

Incidentally, the structure of this embodiment can be easily realized inaccordance with the manufacturing steps of the embodiment 1, and withrespect to the TFT structure or the like, the description of theembodiment 1 or FIG. 1 may be referred to.

Embodiment 3

In this embodiment, a case where a pixel portion having a structuredifferent from FIG. 1 will be described with reference to FIG. 11.Incidentally, steps up to a step of forming a second interlayerinsulating film 44 may be carried out in accordance with theembodiment 1. Since a switching TFT 201 and a current controlling TFT202 covered with the second interlayer insulating film 44 have the samestructure as that in FIG. 1, the description here is omitted.

In the case of this embodiment, after a contact hole is formed throughthe second passivation film 45, the second interlayer insulating film44, and the first passivation film 41, a pixel electrode 51 and banks103 a and 103 b are formed, and then, a cathode 52 and an EL layer 53are formed. In this embodiment, after the cathode 52 is formed by vacuumevaporation, the EL layer 53 is formed by an ink-jet method withoutexposure to the air while a dried inert atmosphere is kept. At thistime, a red light emitting EL layer, a green light emitting EL layer,and a blue light emitting EL layer are formed in different pixels by thebanks 103 a and 103 b. Incidentally, although only one pixel is shown inFIG. 11, pixels having the same structure are formed correspondingly tothe respective colors of red, green and blue, and accordingly colordisplay can be made. A well-known material may be adopted for the ELlayer of each color.

In this embodiment, an aluminum alloy film (aluminum film containingtitanium of 1 wt %) having a thickness of 150 nm is provided as thepixel electrode 51. As a material of the pixel electrode, although anymaterial may be used as long as it is a metal material, it is preferablethat the material has high reflectivity. A MgAg electrode having athickness of 230 nm is used as the cathode 52, and the thickness of theEL layer 53 is made 90 nm (from the bottom, an electron transportinglayer having a thickness of 20 nm, a light emitting layer having athickness of 40 nm, and a hole transporting layer having a thickness of30 nm).

Next, an anode 54 made of a transparent conductive film (in thisembodiment, an ITO film) is formed to a thickness of 110 nm. In thisway, an EL element 209 is formed, and when a third passivation film 55is formed by a material shown in the embodiment 1, the pixel having thestructure as shown in FIG. 11 is completed.

In the case where the structure of this embodiment is adopted, red,green or blue light generated in each pixel is radiated to a sideopposite to the substrate on which the TFT is formed. Thus, almost allregions in the pixel, that is, even the region where the TFT is formedcan also be used as an effective light emitting region. As a result, aneffective light emitting area of the pixel is greatly improved, and thebrightness and contrast ratio (ratio of light to shade) of an image isincreased.

Note that the structure of this embodiment can be freely combined withany of the embodiments 1 and 2.

Embodiment 4

A case of forming a pixel having a structure which differs from that ofFIG. 2 of embodiment 1 is explained in embodiment 4 using FIGS. 12A and12B.

In FIG. 12A, reference numeral 1201 denotes a switching TFT, whichcomprises an active layer 56, a gate electrode 57 a, a gate wiring 57 b,a source wiring 58, and a drain wiring 59. Further, reference numeral1202 denotes a current control TFT, which comprises an active layer 60,a gate electrode 61, a source wiring 62, and a drain wiring 63. Thesource wiring 62 of the current control TFT 1202 is connected to acurrent supply line 64, and the drain wiring 63 is connected to an ELelement 65. FIG. 12B shows the circuit composition of this pixel.

The different point between FIG. 12A and FIG. 2A is the structure of theswitching TFT. In embodiment 4 the gate electrode 57 a is formed with afine line width between 0.1 and 5 μm, and the active layer 56 is formedso as transverse that portion. The gate wiring 57 b is formed so as toelectrically connect the gate electrode 57 a of each pixel. A triplegate structure which does not monopolize much surface area is thusrealized.

Other portions are similar to those of FIG. 2A, and the effectiveemitting surface area becomes larger because the surface areaexclusively used by the switching TFT becomes smaller if the structureof embodiment 4 is employed. In other words, the image brightness isincreased. Furthermore, a gate structure in which redundancy isincreased in order to reduce the value of the off current can berealized, and therefore the image quality can be increased even further.

Note that, in the constitution of embodiment 4, the current supply line64 can be made common between neighboring pixels, as in embodiment 2,and that a structure like that of embodiment 3 may also be used.Furthermore, processes of manufacturing may be performed in accordancewith those of embodiment 1.

Embodiment 5

Cases in which a top gate type TFT is used are explained in embodiments1 to 4, and the present invention may also be implemented using a bottomgate type TFT. A case of implementing the present invention by using areverse stagger type TFT is explained in embodiment 5 using FIG. 13.Note that, except for the structure of the TFT, the structure is thesame as that of FIG. 1, and therefore the same symbols as those of FIG.1 are used when necessary.

In FIG. 13, the similar materials as those of FIG. 1 can be used in thesubstrate 11 and in the base film 12. A switching TFT 1301 and a currentcontrol TFT 1302 are then formed on the base film 12.

The switching TFT 1301 comprises: gate electrodes 70 a and 70 b; a gatewiring 71; a gate insulating film 72; a source region 73; a drain region74; LDD regions 75 a to 75 d; a high concentration impurity region 76;channel forming regions 77 a and 77 b; channel protecting films 78 a and78 b; a first interlayer insulating film 79; a source wiring 80; and adrain wiring 81.

Further, the current control TFT 1302 comprises: a gate electrode 82;the gate insulating film 72; a source region 83; a drain region 84; anLDD region 85; a channel forming region 86; a channel protecting film87; a first interlayer insulating film 79; a source wiring 88; and adrain wiring 89. The gate electrode 82 is electrically connected to thedrain wiring 81 of the switching TFT 1301 at this point.

Note that the above switching TFT 1301 and the current control TFT 1302may be formed in accordance with a known method of manufacturing areverse stagger type TFT. Further, similar materials used incorresponding portions of the top gate type TFTs of embodiment 1 can beused for the materials of each portion (such as wirings, insulatingfilms, and active layers) formed in the above TFTs. Note that thechannel protecting films 78 a, 78 b, and 87, which are not in theconstitution of the top gate type TFT, may be formed by an insulatingfilm containing silicon. Furthermore, regarding the formation ofimpurity regions such as the source regions, the drain regions, and theLDD regions, they may be formed by using a photolithography techniqueand individually changing the impurity concentration.

When the TFTs are completed, a pixel having an EL element 1303 in whichthe first passivation film 41, the second interlayer insulating film(leveling film) 44, the second passivation film 45, the pixel electrode(anode) 46, banks 101 a and 101 b, the EL layer 47, the MgAg electrode(cathode) 48, the aluminum electrode (protecting film) 49, and the thirdpassivation film 50 are formed in order, is completed. Embodiment 1 maybe referred to with respect to manufacturing processes and materials forthe above.

Note that it is possible to freely combine the constitution ofembodiment 5 with the constitution of any of embodiments 2 to 4.

Embodiment 6

It is effective to use a material having a high thermal radiatingeffect, similar to that of the second passivation film 45, as the basefilm formed between the active layer and the substrate in the structuresof FIG. 5C of embodiment 1 or FIG. 1. In particular, a large amount ofcurrent flows in the current control TFT, and therefore heat is easilygenerated, and deterioration due to self generation of heat can become aproblem. Thermal deterioration of the TFT can be prevented by using thebase film of embodiment 6, which has a thermal radiating effect, forthis type of case.

The effect of protecting from the diffusion of mobile ions from thesubstrate is also very important, of course, and therefore it ispreferable to use a lamination structure of a compound including Si, Al,N, O, and M, and an insulating film containing silicon, similar to thefirst passivation film 41.

Note that it is possible to freely combine the constitution ofembodiment 6 with the constitution of any of embodiments 1 to 5.

Embodiment 7

When the pixel structure shown in embodiment 3 is used, the lightemitted from the EL layer is radiated in the direction opposite to thesubstrate, and therefore it is not necessary to pay attention to thetransmissivity of materials, such as the insulating film, which existbetween the substrate and the pixel electrode. In other words, materialswhich have a somewhat low transmissivity can also be used.

It is therefore advantageous to use a carbon film, such as a diamondthin film, a diamond-like carbon film, or an amorphous carbon film, asthe base film 12, the first passivation film 41 or the secondpassivation film 45. In other words, because it is not necessary toworry about lowering the transmissivity, the film thickness can be setthick, to between 100 and 500 nm, and it is possible to have a very highthermal radiating effect.

Regarding the use of the above carbon films in the third passivationfilm 50, note that a reduction in the transmissivity must be avoided,and therefore it is preferable to set the film thickness to between 5and 100 nm.

Note that, in embodiment 7, it is effective to laminate with anotherinsulating film when a carbon film is used in any of the base film 12,the first passivation film 41, the second passivation film 49, or thethird passivation film 50.

In addition, embodiment 7 is effective when the pixel structure shown inembodiment 3 is used, and for other constitutions, it is possible tofreely combine the constitution of embodiment 7 with the constitution ofany of embodiments 1 to 6.

Embodiment 8

The amount of the off current value in the switching TFT in the pixel ofthe EL display device is reduced by using a multi-gate structure for theswitching TFT, and the present invention is characterized by theelimination of the need for a storage capacitor. This is a device formaking good use of the surface area, reserved for the storage capacitor,as an emitting region.

However, even if the storage capacitor is not completely eliminated, aneffect of increasing the effective emitting surface area, by the amountthat the exclusive surface area is made smaller, can be obtained. Inother words, the object of the present invention can be sufficientlyachieved by reducing the value of the off current by using a multi-gatestructure for the switching TFT, and by only shrinking the exclusivesurface area of the storage capacitor.

It is therefore possible to use a pixel structure such as that shown inFIG. 14. Note that, when necessary, the same symbols are used in FIG. 14as in FIG. 1.

The different point between FIG. 14 and FIG. 1 is the existence of astorage capacitor 1401 connected to the switching TFT. The storagecapacitor 1401 is formed by a semiconductor region (lower electrode)extended from the drain region 14 of the switching TFT 201, the gateinsulating film 18, and a capacitor electrode (upper electrode) 1403.The capacitor electrode 1403 is formed at the same time as the gateelectrodes 19 a, 19 b, and 35 of the TFT.

A top view is shown in FIG. 15A. The cross sectional diagram taken alongthe line A-A′ in the top view of FIG. 15A corresponds to FIG. 14. Asshown in FIG. 15A, the capacitor electrode 1403 is electricallyconnected to the source region 31 of the current control TFT through aconnecting wiring 1404 which is electrically connected to the capacitorelectrode 1403. Note that the connection wiring 1404 is formed at thesame time as the source wirings 21 and 36, and the drain wirings 22 and37. Furthermore, FIG. 15B shows the circuit constitution of the top viewshown in FIG. 15A.

Note that the constitution of embodiment 8 can be freely combined withthe constitution of any of embodiments 1 to 7. In other words, only thestorage capacitor is formed within the pixel, no limitations are addedwith regard to the TFT structure or the EL layer materials.

Embodiment 9

Laser crystallization is used as the means of forming the crystallinesilicon film 302 in embodiment 1, and a case of using a different meansof crystallization is explained in embodiment 9.

After forming an amorphous silicon film in embodiment 9, crystallizationis performed using the technique recorded in Japanese Patent ApplicationLaid-open No. Hei 7-130652. The technique recorded in the above patentapplication is one of obtaining a crystalline silicon film having goodcrystallinity by using an element such as nickel as a catalyst forpromoting crystallization.

Further, after the crystallization process is completed, a process ofremoving the catalyst used in the crystallization may be performed. Inthis case, the catalyst may be gettered using the technique recorded inJapanese Patent Application Laid-open No. Hei 10-270363 or JapanesePatent Application Laid-open No. Hei 8-330602.

In addition, a TFT may be formed using the technique recorded in thespecification of Japanese Patent Application Serial No. Hei 11-076967 bythe applicant of the present invention.

The processes of manufacturing shown in embodiment 1 are one embodimentof the present invention, and provided that the structure of FIG. 1 orof FIG. 5C of embodiment 1 can be realized, then other manufacturingprocess may also be used without any problems, as above.

Note that it is possible to freely combine the constitution ofembodiment 9 with the constitution of any of embodiments 1 to 8.

Embodiment 10

In driving the EL display device of the present invention, analogdriving can be performed using an analog signal as an image signal, anddigital driving can be performed using a digital signal.

When analog driving is performed, the analog signal is sent to a sourcewiring of a switching TFT, and the analog signal, which contains grayscale information, becomes the gate voltage of a current control TFT.The current flowing in an EL element is then controlled by the currentcontrol TFT, the EL element emitting intensity is controlled, and grayscale display is performed. In this case, it is preferable to operatethe current control TFT in a saturation region. In other words, it ispreferable to operate the TFT within the conditions of|V_(ds)|>|V_(gs)−V_(th)|. Note that V_(ds) is the voltage differencebetween a source region and a drain region, V_(gs) is the voltagedifference between the source region and a gate electrode, and V_(th) isthe threshold voltage of the TFT.

On the other hand, when digital driving is performed, it differs fromthe analog type gray scale display, and gray scale display is performedby time division driving (time ratio gray scale driving) or surface arearatio gray scale driving. Namely, by regulating the length of theemission time or the ratio of emitting surface area, color gray scalescan be made to be seen visually as changing. In this case, it ispreferable to operate the current control TFT in the linear region. Inother words, it is preferable to operate the TFT within the conditionsof |V_(ds)|<|V_(gs)−V_(th)|.

The EL element has an extremely fast response speed in comparison to aliquid crystal element, and therefore it is possible to have high speeddriving. Therefore, the EL element is one which is suitable for timeratio gray scale driving, in which one frame is partitioned into aplural number of subframes and then gray scale display is performed.Furthermore, it has the advantage of the period of one frame beingshort, and therefore the amount of time for which the gate voltage ofthe current control TFT is maintained is also short, and a storagecapacitor can be made smaller or eliminated.

The present invention is a technique related to the element structure,and therefore any method of driving it may thus be used.

Embodiment 11

In embodiment 11, examples of the pixel structure of the EL displaydevice of the present invention are shown in FIGS. 23A and 23B. Notethat in embodiment 11, reference numeral 4701 denotes a source wiring ofa switching TFT 4702, reference numeral 4703 denotes a gate wiring ofthe switching TFT 4702, reference numeral 4704 denotes a current controlTFT, 4705 denotes an electric current supply line, 4706 denotes a powersource control TFT, 4707 denotes a power source control gate wiring, and4708 denotes an EL element. Japanese Patent Application Serial No. Hei11-341272 may be referred to regarding the operation of the power sourcecontrol TFT 4706.

Further, in embodiment 11 the power source control TFT 4706 is formedbetween the current control TFT 4704 and the EL element 4708, but astructure in which the current control TFT 4704 is formed between thepower source control TFT 4706 and the EL element 4708 may also be used.In addition, it is preferable for the power source control TFT 4706 tohave the same structure as the current control TFT 4704, or for both tobe formed in series by the same active layer.

FIG. 23A is an example of a case in which the electric current supplyline 4705 is common between two pixels. Namely, this is characterized inthat the two pixels are formed having linear symmetry around theelectric current supply line 4705. In this case, the number of electriccurrent supply lines can be reduced, and therefore the pixel portion canbe made even more high precision.

Furthermore, FIG. 23B is an example of a case in which an electriccurrent supply line 4710 is formed parallel to the gate wiring 4703, andin which a power source control gate wiring 4711 is formed parallel tothe source wiring 4701. Note that in FIG. 23B, the structure is formedsuch that the electric current supply line 4710 and the gate wiring 4703do not overlap, but provided that both are wirings formed on differentlayers, then they can be formed to overlap, sandwiching an insulatingfilm. In this case, the exclusive surface area of the electric currentsupply line 4710 and the gate wiring 4703 can be shared, and the pixelsection can be made even more high precision.

Embodiment 12

In embodiment 12, examples of the pixel structure of the EL displaydevice of the present invention are shown in FIGS. 24A and 24B. Notethat in embodiment 12, reference numeral 4801 denotes a source wiring ofa switching TFT 4802, reference numeral 4803 denotes a gate wiring ofthe switching TFT 4802, reference numeral 4804 denotes a current controlTFT, 4805 denotes an electric current supply line, 4806 denotes anerasure TFT, 4807 denotes an erasure gate wiring, and 4808 denotes an ELelement. Japanese Patent Application Serial No. Hei 11-338786 may bereferred to regarding the operation of the erasure TFT 4806.

The drain of the erasure TFT 4806 is connected to a gate of the currentcontrol TFT 4804, and it becomes possible to forcibly change the gatevoltage of the current control TFT 4804. Note that an n-channel TFT or ap-channel TFT may be used for the erasure TFT 4806, but it is preferableto make it the same structure as the switching TFT 4802 so that the offcurrent value can be made smaller.

FIG. 24A is an example of a case in which the electric current supplyline 4805 is common between two pixels. Namely, this is characterized inthat the two pixels are formed having linear symmetry around theelectric current supply line 4805. In this case, the number of electriccurrent supply lines can be reduced, and therefore the pixel section canbe made even more high precision.

In addition, FIG. 24B is an example of a case in which an electriccurrent supply line 4810 is formed parallel to the gate wiring 4803, andin which an erasure gate wiring 4811 is formed parallel to the sourcewiring 4801. Note that in FIG. 24B, the structure is formed such thatthe electric current supply line 4810 an the gate wiring 4803 do notoverlap, but provided that both are wirings formed on different layers,then they can be formed to overlap, sandwiching an insulating film. Inthis case, the exclusive surface area of the electric current supplyline 4810 and the gate wiring 4803 can be shared, and the pixel sectioncan be made even more high precision.

Embodiment 13

The EL display device of the present invention may have a structure inwhich several TFTs are formed within a pixel. In embodiments 11 and 12,examples of forming three TFTs are shown, but from 4 to 6 TFTs may alsobe formed. It is possible to implement the present invention withoutplacing any limitations on the structure of the pixels of the EL displaydevice.

Embodiment 14

An example of using a p-channel TFT as the current control TFT 202 ofFIG. 1 is explained in embodiment 14. Note that other portions are thesame as those of FIG. 1, and therefore a detailed explanation of theother portions is omitted.

A cross sectional structure of the pixel of embodiment 14 is shown inFIG. 25. Embodiment 1 may be referred to for a method of manufacturingthe p-channel TFT used in embodiment 14. An active layer of thep-channel TFT comprises a source region 2801, a drain region 2802, and achannel forming region 2803, and the source region 2801 is connected tothe source wiring 36, and the drain region 2802 is connected to thedrain wiring 37.

For cases in which the anode of an EL element is connected to thecurrent control TFT, it is preferable to use the p-channel TFT as thecurrent control TFT.

Note that it is possible to implement the constitution of embodiment 14by freely combining it with the constitution of any of embodiments 1 to13.

Embodiment 15

By using an EL material in which phosphorescence from a triplet stateexciton can be utilized in light emission in embodiment 15, the externalemission quantum efficiency can be increased by a great amount. By doingso, it becomes possible to make the EL element into a low powerconsumption, long life, and low weight EL element.

Reports of utilizing triplet state excitons and increasing the externalemission quantum efficiency is shown in the following papers.

Tsutsui, T., Adachi, C., and Saito, S., Photochemical Processes inOrganized Molecular Systems, Ed. Honda, K., (Elsevier Sci. Pub., Tokyo,1991), p. 437.

The molecular formula of the EL material (coumarin pigment) reported inthe above paper is shown below.

[Chem 11]

Baldo, M. A., O'Brien, D. F., You, Y., Shoustikov, A., Sibley, S.,Thompson, M. E., and Forrest, S. R., Nature 395 (1998) p. 151.

The molecular formula of the EL material (Pt complex) reported in theabove paper is shown below.

[Chem 12]

Baldo, M. A., Lamansky, S., Burrows, P. E., Thompson, M. E., andForrest, S. R., Appl. Phys. Lett., 75 (1999) p. 4.

Tsutui, T., Yang, M. J., Yahiro, M., Nakamura, K., Watanabe, T., Tsuji,T., Fukuda, Y., Wakimoto, T., Mayaguchi, S., Jpn. Appl. Phys., 38 (12B)(1999) L1502.

The molecular formula of the EL material (Ir complex) reported in theabove paper is shown below.

[Chem 13]

Provided that the phosphorescence emission from triplet state excitonscan be utilized, then in principle it is possible to realize an externalemission quantum efficiency which is 3 to 4 times higher than that forcases of using the fluorescence emission from singlet state excitons.Note that it is possible to implement the constitution of embodiment 15by freely combining it with the constitution of any of embodiments 1 to13.

Embodiment 16

In embodiment 1 it is preferable to use an organic EL material as an ELlayer, but the present invention can also be implemented using aninorganic EL material. However, current inorganic EL materials have anextremely high driving voltage, and therefore a TFT which has voltageresistance characteristics that can withstand the driving voltage mustbe used in cases of performing analog driving.

Alternatively, if inorganic EL materials having lower driving voltagesthan conventional inorganic EL materials are developed, then it ispossible to apply them to the present invention.

Further, it is possible to freely combine the constitution of embodiment16 with the constitution of any of embodiments 1 to 14.

Embodiment 17

An active matrix type EL display device (EL module) formed byimplementing the present invention has superior visibility in brightlocations in comparison to a liquid crystal display device because it isa self-emitting type device. It therefore has a wide range of uses as adirect-view type EL display (indicating a display incorporating an ELmodule).

Note that a wide viewing angle can be given as one advantage which theEL display has over a liquid crystal display. The EL display of thepresent invention may therefore be used as a display (display monitor)having a diagonal equal to 30 inches or greater (typically equal to 40inches or greater) for appreciation of TV broadcasts by large screen.

Further, not only can it be used as an EL display (such as a personalcomputer monitor, a TV broadcast reception monitor, or an advertisementdisplay monitor), it can be used as a display for various electronicdevices.

The following can be given as examples of such electronic devices: avideo camera; a digital camera; a goggle type display (head mounteddisplay); a car navigation system; a personal computer; a portableinformation terminal (such as a mobile computer, a mobile telephone, oran electronic book); and an image playback device using a recordingmedium (specifically, a device which performs playback of a recordingmedium and is provided with a display which can display those images,such as a compact disk (CD), a laser disk (LD), or a digital video disk(DVD)). Examples of these electronic devices are shown in FIGS. 16A to16F.

FIG. 16A is a personal computer, comprising a main body 2001, a casing2002, a display portion 2003, and a keyboard 2004. The present inventioncan be used in the display portion 2003.

FIG. 16B is a video camera, comprising a main body 2101, a displayportion 2102, an audio input portion 2103, operation switches 2104, abattery 2105, and an image receiving portion 2106. The present inventioncan be used in the display portion 2102.

FIG. 16C is a goggle display, comprising a main body 2201, a displayportion 2202, and an arm portion 2203. The present invention can be usedin the display portion 2202.

FIG. 16D is a mobile computer, comprising a main body 2301, a cameraportion 2302, an image receiving portion 2303, operation switches 2304,and a display portion 2305. The present invention can be used in thedisplay portion 2305.

FIG. 16E is an image playback device (specifically, a DVD playbackdevice) provided with a recording medium, comprising a main body 2401, arecording medium (such as a CD, an LD, or a DVD) 2402, operationswitches 2403, a display portion (a) 2404, and a display portion (b)2405. The display portion (a) is mainly used for displaying imageinformation, and the image portion (b) is mainly used for displayingcharacter information, and the present invention can be used in theimage portion (a) 2404 and in the image portion (b) 2405. Note that thepresent invention can be used as an image playback device provided witha recording medium in devices such as a CD playback device and gameequipment.

FIG. 16F is an EL display, containing a casing 2501, a support stand2502, and a display portion 2503. The present invention can be used inthe display portion 2503. The EL display of the present invention isespecially advantageous for cases in which the screen is made large, andis favorable for displays having a diagonal greater than or equal to 10inches (especially one which is greater than or equal to 30 inches).

Furthermore, if the emission luminance of EL materials becomes higher infuture, then it will become possible to use the present invention in afront type or a rear type projector.

The above electronic devices are becoming more often used to displayinformation provided through an electronic transmission circuit such asthe Internet or CATV (cable television), and in particular,opportunities for displaying animation information are increasing. Theresponse speed of EL materials is extremely high, and therefore ELdisplays are suitable for performing this type of display.

The emitting portion of the EL display device consumes power, andtherefore it is preferable to display information so as to have theemitting portion become as small as possible. Therefore, when using theEL display device in a display portion which mainly displays characterinformation, such as a portable information terminal, in particular, aportable telephone of a car audio system, it is preferable to drive itby setting non-emitting portions as background and forming characterinformation in emitting portions.

FIG. 22A is a portable telephone, comprising a main body 2601, an audiooutput portion 2602, an audio input portion 2603, a display portion2604, operation switches 2605, and an antenna 2606. The EL displaydevice of the present invention can be used in the display portion 2604.Note that by displaying white characters in a black background in thedisplay portion 2604, the power consumption of the portable telephonecan be reduced.

FIG. 22B is an on-board audio system (car audio system), containing amain body 2701, a display portion 2702, and operation switches 2703 and2704. The EL display device of the present invention can be used in thedisplay portion 2702. Furthermore, an on-board audio system is shown inembodiment 17, but a desktop type audio system may also be used. Notethat by displaying white characters in a black background in the displayportion 2702, the power consumption can be reduced.

The range of applications of the present invention is thus extremelywide, and it is possible to apply the present invention to electronicdevices in all fields. Furthermore, the electronic devices of embodiment17 can be realized by using any constitution of any combination ofembodiments 1 to 16.

By using the present invention, it becomes possible to suppressdegradation of EL elements due to moisture and heat. Further, thepresent invention can prevent imposing bad influence on TFT performanceby diffusion of alkali metals from the EL layer. As a result, theoperation performance and reliability can be greatly enhanced.

Moreover, it becomes possible to produce application products(electronic devices) having good image quality and durable (highlyreliable) by comprising such EL display device as a display.

1. A method for manufacturing an electro-optical device comprising:forming a thin film transistor having multi-gate structure on aninsulating surface; forming a passivation film over the thin filmtransistor; forming a first electrode over the passivation film, thefirst electrode electrically connected to the thin film transistor;forming an EL layer over the first electrode through an ink jet method;and forming a second electrode over the EL layer.
 2. The methodaccording to claim 1, wherein the thin film transistor functions as aswitching element.
 3. The method according to claim 1, furthercomprising: forming a bank comprising a resin over the first electrode.4. The method according to claim 1, wherein the EL layer comprises anorganic material.
 5. The method according to claim 1, wherein the inkjet method uses a piezo element.
 6. The method according to claim 1,wherein the second electrode comprises at least one selected from thegroup consisting of magnesium (Mg), lithium (Li), cesium (Cs), barium(Ba), potassium (K), beryllium (Be), and calcium (Ca).
 7. The methodaccording to claim 1, further comprising: forming a contact hole in thepassivation film and at least one insulating film in the thin filmtransistor, wherein an upper diameter of the contact hole is longerlength than a lower diameter of the contact hole.
 8. The methodaccording to claim 1, further comprising: forming a contact hole in thepassivation film and at least one insulating film in the thin filmtransistor, wherein the first electrode is in contact with side surfacesof the contact hole and edges of the passivation film.
 9. A method formanufacturing an electro-optical device comprising: forming a thin filmtransistor having multi-gate structure on an insulating surface; forminga passivation film over the thin film transistor; forming a firstelectrode over the passivation film, the first electrode electricallyconnected to the thin film transistor; forming an EL layer over thefirst electrode through an ink jet method; and forming a secondelectrode over the EL layer, wherein the EL layer and the secondelectrode are continuously formed without opening to an air.
 10. Themethod according to claim 9, wherein the thin film transistor functionsas a switching element.
 11. The method according to claim 9, furthercomprising: forming a bank comprising a resin over the first electrode.12. The method according to claim 9, wherein the EL layer comprises anorganic material.
 13. The method according to claim 9, wherein the inkjet method uses a piezo element.
 14. The method according to claim 9,wherein the second electrode comprises at least one selected from thegroup consisting of magnesium (Mg), lithium (Li), cesium (Cs), barium(Ba), potassium (K), beryllium (Be), and calcium (Ca).
 15. The methodaccording to claim 9, further comprising: forming a contact hole in thepassivation film and at least one insulating film in the thin filmtransistor, wherein an upper diameter of the contact hole is longerlength than a lower diameter of the contact hole.
 16. The methodaccording to claim 9, further comprising: forming a contact hole in thepassivation film and at least one insulating film in the thin filmtransistor, wherein the first electrode is in contact with side surfacesof the contact hole and edges of the passivation film.
 17. A method formanufacturing an electro-optical device comprising: forming a thin filmtransistor having multi-gate structure on an insulating surface; forminga first passivation film over the thin film transistor; forming a firstelectrode over the passivation film, the first electrode electricallyconnected to the thin film transistor; forming an EL layer over thefirst electrode through an ink jet method; forming a second electrodeover the EL layer; and forming a second passivation film over the secondelectrode.
 18. The method according to claim 17, wherein the thin filmtransistor functions as a switching element.
 19. The method according toclaim 17, further comprising: forming a bank comprising a resin over thefirst electrode.
 20. The method according to claim 17, wherein the ELlayer comprises an organic material.
 21. The method according to claim17, wherein the ink jet method uses a piezo element.
 22. The methodaccording to claim 17, wherein the second electrode comprises at leastone selected from the group consisting of magnesium (Mg), lithium (Li),cesium (Cs), barium (Ba), potassium (K), beryllium (Be), and calcium(Ca).
 23. The method according to claim 17, further comprising: forminga contact hole in the passivation film and at least one insulating filmin the thin film transistor, wherein an upper diameter of the contacthole is longer length than a lower diameter of the contact hole.
 24. Themethod according to claim 17, further comprising: forming a contact holein the passivation film and at least one insulating film in the thinfilm transistor, wherein the first electrode is in contact with sidesurfaces of the contact hole and edges of the passivation film.
 25. Amethod for manufacturing an electro-optical device comprising: forming athin film transistor having multi-gate structure on an insulatingsurface; forming a first passivation film over the thin film transistor;forming a first electrode over the passivation film, the first electrodeelectrically connected to the thin film transistor; forming an EL layerover the first electrode through an ink jet method; forming a secondelectrode over the EL layer; and forming a second passivation film overthe second electrode, wherein the EL layer, the second electrode and thesecond passivation film are continuously formed without opening to anair.
 26. The method according to claim 25, wherein the thin filmtransistor functions as a switching element.
 27. The method according toclaim 25, further comprising: forming a bank comprising a resin over thefirst electrode.
 28. The method according to claim 25, wherein the ELlayer comprises an organic material.
 29. The method according to claim25, wherein the ink jet method uses a piezo element.
 30. The methodaccording to claim 25, wherein the second electrode comprises at leastone selected from the group consisting of magnesium (Mg), lithium (Li),cesium (Cs), barium (Ba), potassium (K), beryllium (Be), and calcium(Ca).
 31. The method according to claim 25, further comprising: forminga contact hole in the passivation film and at least one insulating filmin the thin film transistor, wherein an upper diameter of the contacthole is longer length than a lower diameter of the contact hole.
 32. Themethod according to claim 25, further comprising: forming a contact holein the passivation film and at least one insulating film in the thinfilm transistor, wherein the first electrode is in contact with sidesurfaces of the contact hole and edges of the passivation film.